The conventional fluid passage connectors for such tubing are typically of the type that a connecting opening formed in the main body of a metallic joint is partly tapered inwardly, and said inwardly tapered portion is engaged in a fluid-tight manner with a holder member fixed in the vicinity of the end of a tube to be connected, i.e., a metallic ferrule in a conical and ring-like form, with the use of an engaging member such as a push bolt for the sealing purpose.
For example, FIG. 1 is a view illustrative of the arrangement of a typical analyzer, in which a sample inject valve 1 is connected to a movable sample inject valve 4 having sample reservoir loops 2 and 3, and is further connected to with a sample intake tube 5 and a connecting tube 7 for suction means 6 at diametrically opposed positions. The arrangement also has a solvent supply tube 10 leading to a solvent reservoir 9 equipped with a solvent supply pump 8, and a connecting tube 12 for a column 11 at diametrically opposed positions, column 11 is connected with a UV-ray absorbing monitor 14 by way of a tube 13. Furthermore, the monitor 14 is electrically connected with a recorder 15 to record data.
As shown in FIG. 2, the conventional fluid passage connector for tubing used with such a chromatograph is typically of the type that a connecting opening 17 formed in the main body 16 of a metallic joint is partly provided with an inwardly tapered face 18, a tube 20 is inserted through a push bolt 21, said tube 20 being fixedly provided with a metallic ferrule 19 in the vicinity of the lower end thereof, said ferrule 19 combining a tube holding member with a sealing member, and the push bolt 21 is engaged with an internally threaded portion 22 of said connecting opening 17, followed by clamping with a large torque with the use of a tool such as a wrench, whereby the end edge of the ferrule 19 is engaged with the tapered face 18 of said connecting opening 17 for sealing.
Moreover, the tube 20 is fitted at its end into the deepest space 23 of the connecting opening 17, and a fluid passage 25 is open at the bottom 24 of the tube 20. In addition, the end portion of the tube 20 slightly projects from the end portion of the metallic ferrule 19. Furthermore, it is impossible to exclude completely the tube fitting space 23 between the deepest portion of the connecting opening 17 and the top of tube 20. In consequence, there is formed a gap 26 around the end of the tube 20. A sample molecule or solvent diffuses into or out from that gap 26 during analysis, thus forming a dead volume and posing a grave bar to an efficient separation. When it is desired to obtain as a result of accurate analysis a chart having a separation peak 27 of a normal width W, as shown in FIG. 3(A), it is likely that the width W' of a separation peak 27' may become wide, as shown in FIG. 3 (B), tailing 28 may take place, leading to unsatisfactory separation, and the height of a peak may vary, resulting in the base line being unreliable. Thus, the prior art is disadvantageous in that no accurate analytical data of good reproductivity are obtained. Such a disadvantage becomes further marked, when there are an increasing number of connections.
It is further required to hold the push bolt 21 in place with a greater torque by screwing or other means, since sealing is effected with the metallic ferrule 19 and the tapered face 18 of the main body 16 of the metallic joint. This needs a special tool such as a wrench. The application of a still greater torque to screw the bolt 21 in place may cause deformation of the tube 20 and, hence, a reduction in the cross-sectional area of the fluid passages 25. Thus, the prior art is unsuitable for use in the connection of flexible tubes.
From now on, there will be an increasing tendency toward the use of highly sensitive microanalysis, and the presence of a dead volume in each joint will cause a further important problem.